Many elongated medical devices are known that are inserted through an access pathway into a body vessel, organ or cavity to locate a therapeutic or diagnostic distal segment of the elongated medical device into alignment with an anatomic feature of interest. For example, catheters, introducers and guide sheaths of various types, drainage tubes, and cannulas are available that extend from outside the body through an access pathway to a site of interest and provide a lumen through which fluids, materials, or other elongated medical devices are introduced to the site or body fluids are drained or sampled from the site. Other elongated medical devices include many forms of medical electrical leads that bear sensing and/or electrical stimulation electrodes for sensing electrical signals of the body and/or applying electrical stimulation to the body, e.g. leads for pacing, cardioversion, nerve stimulation, muscle stimulation, spinal column stimulation, deep brain stimulation, etc. Other medical electrical leads bearing physiologic sensors for measuring pressure, temperature, pH, etc, in a distal segment thereof that are adapted to be placed at a site of interest are also known. Other elongated medical devices include guide wires that are directed through tortuous vascular pathways to locate a distal segment thereof typically within a blood vessel. A catheter, e.g. a PTCA balloon catheter for dilating constrictions in blood vessels or delivering stents and grafts or a medical electrical lead having a through-lumen are then advanced over-the-wire to the site. Further elongated medical devices include stiffening stylets that are placed into the lumens of medical electrical leads and in certain guide wires to impart column strength and stiffness to the assembly to enable its transvenous advancement into a heart chamber or cardiac blood vessel.
Such elongated medical devices must have flexibility to navigate the twists and turns of the access pathway, sufficient column strength in the proximal segment thereof to be pushed through the access pathway alone or over a guide wire or through a lumen, and the capability of orienting the distal segment and any electrodes or sensors or ports of the distal segment in a preferred alignment with an anatomical feature at the accessed site so that a diagnostic or therapeutic procedure can be completed. In general terms, the elongated medical device body must also resist kinking and be capable of being advanced through access pathways that twist and turn, sometimes abruptly at acute angles.
It is commonly the practice with certain guide catheters and diagnostic catheters to provide preformed bends at the junctions between segments or pre-curved or shaped segments that are adapted to orient the distal segment and possibly intermediate segments into alignment with an anatomical feature at the accessed site. For instance, many diagnostic procedures involve placing a catheter tip into or a side port across a vascular orifice to inject radiographic fluid through the catheter lumen into the vessel. Such diagnostic catheters have historically been formed of thermoplastic materials that can be heated as in heated water and bent into a shape that the physician can use in attempting to access the vessel opening. A considerable variety of pre-formed shapes of such catheters have been developed over the years and made available for use in such procedures. Still, the physician may find that the anatomy of any given patient may require altering the bend by heating the catheter, changing the bend and letting it cool before it is advanced to the site where it must make an abrupt change in direction.
The distal segment of a catheter that facilitates the delivery of other medical devices, fluids, drugs, diagnostic agents, or the like, through tortuous pathways of the body frequently needs to be selectively deflected or bent and straightened again while being advanced within the patient to steer the catheter distal end into a desired body lumen or heart chamber or branching blood vessel. Such selective deflection is accomplished by advancing the guide catheter over a previously placed guide wire via a guide wire lumen or by insertion of removable stiffening stylets shaped to impart a selected bend in the distal segment into a stylet lumen or by a steerable mechanism permanently built into the catheter body. Such catheters are referred to herein collectively as “steerable catheters” employing “deflection mechanisms” regardless of use.
For example, commonly assigned U.S. Pat. Nos. 6,280,433 and 6,379,346 disclose steerable catheters that are employed to access the a blood vessel through a percutaneous incision and to be advanced to a site within the vascular system or a heart chamber. A bitumen catheter body is disclosed that comprises a relatively large diameter delivery lumen and a smaller diameter stylet lumen that is blocked at its distal end. The deflection mechanism in this case comprises a stiffening stylet that can be selectively introduced into and removed from the stylet lumen from a proximal hub or handle. The stiffening stylet is advanced distally until the stylet distal end abuts the stylet lumen end to stiffen the catheter body to aid its introduction and advancement. The stylet distal end can be shaped when outside the stylet lumen opening to impart a curve to the catheter body when inserted into the lumen to assist in steering the catheter distal end through the pathway. The stylet lumen is preferably lined with a wire coil sheath, and the handle and delivery lumen are preferably splittable to aid in removing the introducer catheter from an electrical medical lead introduced through the delivery lumen.
Guide wires introduced through the vasculature to access a remote site in a blood vessel or heart chamber or the like constitute a removable form of deflection mechanism to guide introduction of a steerable catheter over-the-wire to locate catheter body distal end at the remote site. A multi-lumen steerable catheter adapted to be introduced through the vasculature over an earlier introduced, small diameter guide wire is disclosed, for example, in U.S. Pat. No. 6,004,310. A small diameter guide wire lumen and larger diameter delivery lumen extend side-by-side through the length of the catheter body. The small diameter guide wire lumen is also surrounded by and reinforced with a wire braid tube or a coiled wire.
One form of a deflection mechanism built into the catheter body to selectively induce a bend in a distal segment or segments comprises the use of heat activated shape memory alloy members that are built into deflection lumens of a steerable catheter distal segment and that change shape to induce or release bends in the catheter body distal segment depending upon their temperature. The shape memory alloy members can be selectively resistance heated to a temperature above body temperature as disclosed in U.S. Pat. No. 4,776,844, for example, to induce a bend in the distal segment of the steerable catheter.
Another form of a deflection mechanism built into the catheter body comprises the use of a deflection mechanism, referred to as control lines or reins or deflection wires or push-pull wires or pull wires (herein “pull wires”), extending between a proximal handle through proximal and distal segments of the catheter body to a point of attachment of the pull wire distal end to the distal segment. The deflection mechanism is manipulated to selectively deflect or straighten the distal segment and, in some cases, intermediate segments of the catheter body. More complex steerable catheters have two or more pull wire lumens and pull wires extending from the handle through the pull wire lumens to different points along the length or about the circumference of the catheter body to induce bends in multiple segments of the catheter body and/or in different directions. In addition, even more complex steerable catheters are known that incorporate one or more distal electrode or sensor and corresponding conductor or inflatable balloons or other components.
For example, many versions of electrophysiology (EP) catheters have been disclosed that are designed to perform mapping and/or ablation of cardiac tissue to diagnose and treat abnormal tissue that induces or sustains cardiac arrhythmias and that employ deflectable distal and intermediate segments controlled by push-pull or pull wire mechanisms. During an EP ablation or mapping procedure, the steerable distal end of the steerable catheter is used to orient the distal tip of the EP device with respect to tissue, such as a patient's endocardium, to facilitate mapping and/or proper delivery of the device's RF or laser energy to the tissue. Highly complex shapes are sometimes found necessary to encircle a pulmonary vein orifice, for example, to ablate the left atrial wall tissue to interrupt arrhythmic pathways. For example, commonly assigned U.S. Pat. Nos. 5,445,148, 5,545,200, 5,487,757, 5,823,955, and 6,002,955 disclose a variety of such shapes and mechanisms for forming the shapes.
In most simple or complex steerable catheters incorporating pull wire(s), a relatively large diameter delivery lumen and relatively small diameter pull wire lumen(s) (as well as other lumens for conductors or the like) are desirable. At the same time, the outer diameter of the steerable catheter must be minimized so that it can be readily advanced within the patient. Exemplary multi-lumen and bitumen steerable catheters having relatively larger delivery lumens and incorporating pull wires in relatively small pull wire lumens extending alongside the delivery lumens to selectively deflect the distal segment of the catheter are disclosed in U.S. Pat. Nos. 2,688,329, 3,605,725, 4,586,923, 5,030,204, 5,431,168, 5,484,407, 5,571,085,6,217,549, 6,251,092, and 6,371,476, and in published U.S. Patent Appln. Pub. No. 2001/0049491. Many of these exemplary steerable catheters are relatively simple, having only a single pull wire lumen and a delivery lumen extending between proximal and distal lumen end openings for introduction or withdrawal of fluids, or delivery of drugs or other medical devices into the body.
The walls of multi-lumen steerable catheters are necessarily thin in order to maximize the size of the delivery lumen and minimize the outer diameter of the steerable catheter and strong to exhibit column strength and pushability. Consequently, a tubular reinforcement or a metal wire braid reinforcement is employed within at least a proximal segment of the outer wall or sheath of the typical steerable catheter body to stiffen the thin catheter wall as disclosed in many of the above-referenced patents and in commonly assigned U.S. Pat. Nos. 5,738,742 and 5,964,971. The reinforced catheter wall enables torque transmission to the catheter distal end as the proximal end of the catheter outside the patient is rotated.
In the fabrication of such steerable catheters, it is necessary to extend the pull wire from a distal point of attachment proximally through the pull wire lumen extending through the deflectable distal segment and the non-deflectable proximal segment of the catheter body to an exit point so that the pull wire proximal end can be coupled to a steering mechanism of the handle. The proximal ends of the pull wires of such steerable catheters either exit through the side wall of the catheter body at a point distal to the catheter body proximal end, as shown in the above-referenced '030 patent and '49491 application, or from a more proximal end opening of the catheter body and are attached to a handle to be manipulated in use to induce a bend or to straighten the deflectable distal segment of the catheter body. Thus, the handle usually encloses the portion of the catheter body where the proximal end of the pull wire is exposed, and the pull wire proximal end is attached to a pull wire knob or ring that can be manipulated by the user to induce a deflection in the catheter body distal segment to steer it.
The relatively smaller diameter pull wire lumen(s) is typically formed to extend alongside the large diameter delivery lumen, such that both the delivery lumen and pull wire lumen are off-axis from the longitudinal axis of the catheter body when fabrication is completed. In the above-referenced '092 patent, the pull wire lumen is formed within an inner polymeric core contained within the outer sheath wall alongside the delivery lumen. The pull wire distal end is attached to the catheter distal end by a ring that encircles the delivery lumen liner and is embedded in a soft tip of the catheter body. In the above-referenced '4941 publication, the pull wire lumen is formed when the outer sheath wall is formed over and embedding the wire braid and delivery lumen. In the above-referenced '407 and '085 patents, at least the proximal, non-deflectable, segment of the pull wire lumen is lined by a tubular thin-walled metal or plastic sheath. In the above-referenced '168, '476 and '549 patents, the pull wire lumen is defined by the lumen of a coiled wire or wire braid tubing. It is suggested in the '549 patent, referring to FIGS. 24A and 24B, that the coiled wire can be included within a plastic sleeve or liner.
Many approaches to the fabrication of the large diameter delivery lumen and the small diameter pull wire lumens within the wire reinforced outer sheath have been disclosed. The large diameter delivery lumen is typically defined by a delivery lumen liner formed of an elastic material, e.g. PTFE fluoropolymer tubing, as described, for example, in the above-referenced '49491 publication and '092 patent. Typically, reinforced steerable catheter bodies are formed employing a thin wall, PTFE liner to define the delivery lumen, because PTFE is relatively lubricious and crush resistant so that a relatively circular, large diameter, thin wall PTFE liner can provide a large diameter delivery lumen. The PTFE wall surface of a PTFE liner has a very low coefficient of friction when leads, guidewires or other catheters are passed through it particularly through curves in the lumen where contact stresses against the wall surface are greatest. In addition, PTFE has a higher melt temperature than the other thermoplastic polymers used in the catheter construction, which allows thermal reflow processes to be used to reflow other polymers over the PTFE liner. PTFE has a middle durometer that is not too stiff in the distal segments but not too soft in the proximal segments, thus making it suitable to traverse the length of the catheter shaft. While PTFE tubing enjoys these advantages, the use of PTFE tubing in the catheter body distal segment renders the distal segment relatively stiff and difficult to form into a bend employing a pull wire or stylet as described above or to track short radius turns of a guide wire.
Due to PTFE surface characteristics, it is also difficult to bond thermoplastic materials embedding wire braid to the PTFE tubing unless the tubing surface is etched. The above-referenced '092 patent discloses the concepts of terminating the wire braid proximal to the catheter body distal end and molding a softer durometer distal end segment to the catheter body distal end to the distal end of the PTFE delivery lumen liner. This approach further complicates the fabrication process.
In thin wall catheters, the outer jackets on the distal segments rarely go below Shore 35D durometer or flexural modulus of 2000 psi. The stainless steel braid wire used in catheters has tended to go up in temper, effectively increasing how sharp of a bend or how much of a loading is sustained without yielding the wire and kinking/buckling the catheter shaft. The braid wire is not usually the limiting factor in atraumatic tip designs although material condition, wire diameter, number of wires, and braid angle have to be optimized. The stiffness of the PTFE liner within the distal segment constitutes the limiting factor in achieving a highly bendable distal end segment. However, a lumen liner is needed in the distal segment to maintain the integrity of each such lumen. Moreover, the distal segment cannot be made too soft as tip control and feel are then lost.
Consequently, a need remains for a steerable catheter body having a relatively flexible and soft distal segment with a large diameter, crush resistant, delivery lumen that is simple to fabricate and reliable in use. A need remains for a catheter body having a soft distal segment and tip that is less traumatic than current technology while still capable of transmitting enough force and torque to effectively negotiate the catheter to the desired anatomical location.
The design of such steerable catheters must be highly robust to ensure the integrity of the delivery lumen, the reliability of use of the pull wire, and to provide the desired degree of deflection. The fabrication of such bitumen steerable catheter bodies is therefore highly labor intensive and time consuming to consistently achieve these design objectives. Simplification of the fabrication steps and the reduction of assembly time without compromising design objectives remains a desirable goal. The present invention satisfies these and other needs.